Retroviral immunotherapy of cancers in dogs, although providing long-term remissions in dogs with early malignancies, did not prevent eventual relapses. Concentrated retroviruses tested in healthy primates proved innocuous at the time of administration and throughout more than a year of observation. No evidence of viral shedding was observed in the sera, urine or feces of treated dogs. A skin transformation assay for identifying members of families carrying autosomal dominant genes for high cancer risk was 80-100% successful in the initial tests. A follow-up study of 40 specimens derived from cancer syndrome families and provided blindly by Dr. Eldon Gardner was hampered by difficulty in resuscitating his cultures after long-term storage. Duplicate cultures provide to and tested by a collaborative group (Drs. M. Gardner and S. Rasheed) correlated significantly (75-80%) with cancer incidence.